ASPHALT BEHAVIOR AT LOW SERVICE TEMPERATURES. FINAL REPORT

A general review of methods for measuring the stiffness properties of asphalt at temperatures below 77 deg F (25 deg C) is presented. Methods used traditionally for asphalt cement as well as those used in other technologies, such as polymer science, are reviewed. A method that is simple to conduct, suitable for specification use, and suitable for the entire range of stiffness below room temperature was not identified. Models available for predicting low temperature cracking were reviewed and all were considered as requiring further development. Two models were selected for use in the study: Program TC-1 and Lytton's fracture mechanics model. The fracture mechanics model requires considerable work to make it operational, but it shows the most promise; TC-1 provides reasonable answers for most asphalts. Correlations between various parameters related at low temperature cracking indicated that direct measurements such as Fraass brittle point, asphalt stiffness, mix stiffness and strength and DMA data correlate best with cracking potential. A bending beam test for the direct measurement of the low temperature stiffness of asphalt cement is proposed along with the protocol for a field verification trial.